1. Field of the Invention
The invention relates to a semiconductor device, and more particularly, to a semiconductor device having a plug structure with low resistance capacitance (Rc).
2. Description of the Prior Art
In the fabrication of semiconductor integrated circuits (ICs), semiconductor devices are generally connected by several metallic interconnecting layers commonly referred to as multi-level interconnects, and a damascene process is a convenient and predominant method for forming the multi-level interconnects. To meet the need of high integration and high processing speed of semiconductor integrated circuits of nano-scale generations, copper interconnect technology has become an effective solution. In comparison with aluminum or other metals, copper has relatively lower resistivity and fewer reliability concerns, such as electromigration, which may further cooperate with low permittivity (low-k) dielectric materials between those metal interconnects, so as to reduce cross talk and/or resistance-capacitance (RC) delay thereof. Thus, copper interconnect technology has been widely in use in single damascene structure and dual damascene structure processes.
One concern with the use of copper as interconnect material is its diffusion property. To prevent copper from diffusing into the ILD layer, the copper core of the damascene structure is typically encapsulated with a diffusion barrier metal. Typical diffusion barrier metals include tantalum (Ta), tantalum nitride (TaN), titanium nitride (TiN) or titanium (Ti) for encapsulating a copper core. Among these barrier materials, tantalum is more prevalent than others in the semiconductor industry because of its relatively higher thermal reliability and ability to prevent copper diffusion. As the line width shrinks to 65 nm or 45 nm node, it is desirable to form a diffusion barrier with reduced thickness and resistance, while maintaining the ability to prevent copper diffusion. Consequently, how to improve the semiconductor integrated circuit for obtaining efficient performance is still an important issue in the field.